There is a quite frequent bug in iPhone 13 Safari
The user agent Mozilla/5.0 (iPhone; CPU iPhone OS 13_4_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/13.1 Mobile/15E148 Safari/604.1 is generating the majority of bugs to WebClientError as shown by Turnilo
We should see if we can get to the bottom of this error by using a real device, running through smoke tests and monitoring the web console/ network tab for errors to get a sense of the impact. 2hrs playing with an iPhone.
In addition to this I suggest we use User-notice to reach out to community to see if anyone using an iphone on mobile has encountered any bugs recently.